1. Field of the Invention
This invention relates to data transfer methods and data transfer devices that perform data transfer using buses configured by integrated circuit devices. This application is based on patent application No. Hei 9-203606 filed in Japan, the content of which is incorporated herein by reference.
2. Description of the Related Art
Conventionally, as for improvements of bus transfer efficiency, the paper of Japanese Patent Application, Publication No. Hei 5-242017 discloses the technology that performs data transfer between a master unit and a slave unit, as follows:
In the case where response of a target is slow in the slave unit, the master unit does not wait for transmission of data from the slave unit while securing a bus after issuance of a transfer request, but the master unit should certainly release the bus. This technology is applied to the configuration that multiple master units and multiple slave units are connected together by way of the common bus.
With reference to timing charts of FIG. 12A to FIG. 12F, a description will be given with respect to an example of the data transfer method at a continuous read mode for a target whose response is slow. When receiving an access request, the master unit secures a bus, then, the master unit outputs an address to release the bus. At occurrence of a next access factor, the master unit secures the bus again, then, the master unit outputs an address to release the bus. In order to output data whose transfer is requested, the slave unit requests a bus (utilization) right. So, after certainly securing the bus, the slave unit outputs an address and the data. According to the conventional method described above, the release of the bus should be certainly performed, so there occurs a gap in time between the timing to release the bus and the timing to secure the bus. In addition, the master unit is designed to have a capability of merely receiving the data in a duration that the slave unit outputs the data. So, the conventional method suffers from a drawback that the data transfer efficiency should be extremely reduced.
As described above, when the master unit accesses the slave unit, the conventional data transfer method should normally release the bus after the access is completed one time. For this reason, although the slave unit is capable of continuously sending the data to the master unit, the conventional method is incapable of continuously performing data transfer. So, there is a problem that bus utilization efficiency is not so good.